key: cord-0999953-1oqm5u7q
authors: Zhang, Daniel Xin
title: SARS-CoV-2: air/aerosols and surfaces in laboratory and clinical settings
date: 2020-05-07
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2020.05.001
sha: 0d6f09146ab8ae497d0b7fdb5aa6ab79872fbe8f
doc_id: 999953
cord_uid: 1oqm5u7q

nan

Sir,

The pandemic of coronavirus disease 2019 (COVID-19) is known to be caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 1 . SARS-CoV-2 is mainly transmitted through respiratory droplets and close contact based on current evidence 1 . However, a report describing a cluster of COVID-19 cases in a shopping mall postulated the indirect transmission of SARS-CoV-2 potentially via surface contamination of common objects or virus aerosolization in a confined space or spread from asymptomatic infected persons 2 . Combined with previous reports implicating other coronaviruses in super-spreading events and nosocomial outbreaks 3 , researchers are now investigating air/aerosol and fomite transmission as potential transmission routes of SARS-CoV-2. Since SARS-CoV-2 is novel, our understanding of its transmission characteristics remains limited. In very close relation to this context, there are four recent studies representative of current investigation of SARS-CoV-2 in air/aerosols and on surfaces in laboratory and clinical settings [4] [5] [6] [7] .

Under laboratory experimental conditions, van Doremalen et al assessed the stability of SARS-CoV-2 in aerosols and on different surfaces in comparison to that of SARS-CoV-1 6 . In general, SARS-CoV-2 and SARS-CoV-1 shared similar stability properties in aerosols and on various surfaces. SARS-CoV-2 retained viability in aerosols for up to 3 hours while it stayed viable on different surfaces for longer periods ranging from 4 to 72 hours. To be specific, SARS-CoV-2 was most stable on plastic surface, followed by stainless steel, cardboard, and copper surfaces, respectively. Moreover, the stability/viability of SARS-CoV-2 decreased over time both in aerosols and on surfaces. In brief, the study highlights the similarity of SARS-CoV-2 and SARS-CoV-1 in stability and viability in aerosols and on different surfaces, the latter of which can be easily inactivated using common disinfectants 8 . This aspect of the two viruses enlightens us to reiterate previous successful infection prevention and control (IPC) solutions in combating SARS with adaptation to the current COVID-19 situation. However, it should also be noted that the viability and stability of SARS-CoV-2 in aerosols was evaluated under laboratory conditions, which may be greatly different from realworld clinical environment, and thus should be interpreted carefully. Further clinical investigations are required to characterise aerosol transmission as potential transmission route of SARS-CoV-2.

Another three studies examined the clinical settings. To begin with, Ong et al investigated the air and surface presence of SARS-CoV-2 associated with 3 patients in a COVID-19-delicated facility in Singapore, where routine cleaning was performed twice a day in patients' rooms 5 . Most pre-cleaning surface samples showed positive results while post-cleaning samples were all negative, suggesting that routine cleaning appears to be effective in containing surface contamination of SARS-CoV-2. Meanwhile, all the air samples were negative. Later, to extend the cohort of the study, Guo et al included 39 patients in a COVID-19-specialised hospital in Wuhan, China, with 15 in the intensive care unit (ICU) and 24 in a general ward 45 . Sampling was performed between twice-daily routine cleanings. As a result, ICU had more positive results than the general ward in both surface and air samples. This implies that more stringent IPC approaches should be considered in ICU as another clinical study pointed out that SARS-CoV-2 lingered significantly longer with higher viral load in the respiratory samples of patients with severe conditions than in those from patients with mild illness 9 . Lately, another study by Liu et al probed the aerodynamics of SARS-CoV-2 at hospitals in Wuhan, China 7 . In this study, researchers found high SARS-CoV-2 viral RNA levels in aerosols from protective apparel removal rooms for medical staff and a poorly ventilated mobile toilet room for patients. Besides, they also observed that good ventilation and proper disinfection and sterilization protocols can effectively restrain the concentration of SARS-CoV-2 RNA detectable in aerosols. Overall, the above studies shed light on the aerosol and fomite dynamics of SARS-CoV-2 in hospital settings 4, 5, 7 . However, quantitative PCR is the only detection method for SARS-CoV-2 used in the studies 4, 5, 7 , which only validated the presence of viral RNA without giving information of the viral infectivity or viability. Since viral stability or viability holds more association with IPC strategies, additional studies are needed to determine this aspect of SARS-CoV-2 using culture in clinical settings.

From the perspective of airborne/aerosol transmission, inconsistent findings were observed in the above studies [4] [5] [6] [7] . Hence, current evidence is not sufficient to conclude whether this transmission route is viable for SARS-CoV-2 4-7 and further investigations are warranted. On the other hand, a Singapore-based case report showed that either surgical masks or N95 respirators provided enough protection for healthcare workers against SARS-CoV-2, even when aerosol-generating procedures were involved 10 . Nevertheless, it should not be neglected that the report was based on one single patient and that environmental contamination risks and IPC measures can vary greatly from institution to institution. Therefore, we should stay vigilant and not be deterred from proper aerosol precautions. To illustrate, many current guidelines and recommendations prioritise respirators like N95s for aerosol-generating medical procedures as we are facing significant shortages of such PPE 11, 12 . Additional studies elucidating which medical procedures pose higher aerosol risks will help decision making.

With regard to fomite transmission, surface contamination hotspots merit extra attention where virusladen droplets tend to deposit. An instance in point is the air exhaust outlets or vents where both studies showed positive swab samplings 4, 5 . By the same token, toilet rooms for patients should not be ignored. Explicitly, swab samplings from toilet bowl and sink in patient's room were positive 5 with other studies reporting the presence of viral RNA in faecal samples and evidence of suspected gastrointestinal infection 7, 13, 14 . Additionally, the shoes of healthcare workers and the floor can be a hotspot, too. For example, the Singapore-based study found a swab sampling from a shoe front surface was positive with the rest of PPE samples negative 5 . Consistent with this, the Wuhan-based research team found that half of shoe sole swab samples from ICU staff were positive 4 . Furthermore, all the samples from the floor of pharmacy were positive which patients had no access to, implying that the virus may be tracked around on the floor through shoes of healthcare workers 4 . Thus, the cleaning frequency can be increased for the surface contamination hotspots identified and disposable shoe cover or shoe sole disinfection may be incorporated into the contamination control measures.

Even though the accumulation of the virus at hotspots may be troublesome, coronaviruses can be easily inactivated using common disinfectants containing adequate concentration of biocidal agents, such as ethanol, sodium hypochlorite and hydrogen peroxide 15, 16 . In addition, ultraviolet (UV) germicidal irradiation is also proposed to inactivate SARS-CoV-2 17 . However, either disinfectants or UV germicidal irradiation is reserved for disinfection of inanimate surfaces only. Message should be made clear to the general public that ingestion or injection of surface disinfectants or sterilisation of skin using UV irradiation is dangerous and should be strictly prohibited, despite mixed information from various sources.

Altogether, when it comes to containing surface contamination, we are encouraged to take local environmental contamination factors at institutions, such as surface exposure to virus-laden droplets and surface materials, into consideration and make the cleaning and disinfection protocols more context-specific, including frequency and timing of cleaning and selection of disinfectants, as the above studies suggest a differential stability/viability profile of SARS-CoV-2 on various surfaces and imbalanced viral distribution between ICU and general ward as well as preferential accumulation of virus on hotspots 4-6 .

In addition to the potential spreading via aerosol and surface, pre-symptomatic or asymptomatic transmission has been recently recognised to contribute to the rapid and broad spreading of SARS-CoV-2 in healthcare settings. To put this in detail, Arons et al performed a thorough investigation into the spread of SARS-CoV-2 in a skilled nursing facility in the US and emphasised the importance of pre-symptomatic precautions in IPC strategies 18 . As shown in the investigation 18 , over half of the facility residents reported positive, as detected by quantitative PCR, prior to showing symptoms. More importantly, viable virus was isolated from samples of the pre-symptomatic residents. This implies that shedding of viable virus by pre-symptomatic residents may contribute to the rapid and extensive transmission of SARS-CoV-2 in the nursing facility. As the authors concluded, in healthcare settings, symptom-based IPC strategies are insufficient and ineffective to contain the transmission. Thus, more proactive IPC measures should focus on preventing the spread from asymptomatic and pre-symptomatic infections, such as limiting access only to essential personnel, and expanding the scale of quantitative PCR-based testing for staff and patients. Besides, implementing universal face mask-wearing policy in healthcare facilities can be useful, as a recent visualisation experiment demonstrated that face covering significantly lowered the count of forwardmoving droplets during speech uttering and may reduce droplet-associated risks 19 .

In summary, IPC in clinical settings is crucial to winning the battle against SARS-CoV-2, as the emergence of this invisible enemy has posed unprecedented threats and challenges to public health worldwide. Recent studies, in connection with this, have equipped us with several IPC key points in controlling aerosol-and fomite-associated risks. With respect to potential air/aerosol-associated risks, we should exercise vigilance and proper precautions, although current evidence is insufficient to determine the potentiality of airborne or aerosol transmission [4] [5] [6] [7] . For instance, respirators like N95s are recommended for aerosol-generating medical procedures as different guidelines suggest 11, 12 and we need to offer adequate room ventilation plus appropriate disinfection and sterilization to effectively limit the SARS-CoV-2 RNA levels in aerosols 7 . In terms of fomite transmission, routine cleaning is effective in containing surface contamination of SARS-CoV-2 5 , and many common disinfectants as well as UV germicidal irradiation can be used to effectively inactivate the virus [15] [16] [17] .

Moreover, we should make IPC protocols more context-specific with local environmental contamination factors considered, since the virus exhibits differential viral viability dynamics on various surfaces and imbalanced viral distribution among different environments. Expressly, more stringent IPC approaches, including more frequent surface cleaning, should be considered for ICU and other surface contamination hotspots, such as air exhaust outlets/vents, patients' toilet rooms, and shoes of healthcare workers 4, 5 . Apart from potential transmission via aerosol and surface, presymptomatic precautions are crucial to prevent and control the viral spreading in healthcare settings, as emerging evidence showed that pre-symptomatic patients can shed viable virus and contribute to nosocomial infections 18 . Key pre-symptomatic precaution measures include limiting access only to essential personnel, expanding quantitative PCR-based testing for staff and patients, and implementing universal face mask-wearing policy in healthcare facilities. Despite the above, our understanding of SARS-CoV-2 transmission dynamics remains rather incomplete. As we are probing more into this topic and gaining further information, timely exchange of knowledge and experience is highly beneficial and essential for successful COVID-19 containment in healthcare settings globally.

Daniel Xin Zhang 1,2

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